BMW calls this part I'm after an Intermediate Plate (part number 16112309404).  Lots of guys remove this flap from their gas caps, but I want to install one on my K75.  Does anyone have one lying around that could be donated?  

Looks like this (picture from the Intrawebs):

Wish you would have posted before the meet up this morning, I would have brought one with me. Pm me your address and I will send you one.
BTW, it was great to meet some of the forum members as well as you!

Rob, I'd seen references to a fuel tank flap over the years but had never seen one before - what is the intended purpose of the device?

I have two of those in my spare stash. I remove them from every filler cap. If you don't/can't source one relatively locally please let me know.

put one in the mail this morrning

Gaz wrote:Rob, I'd seen references to a fuel tank flap over the years but had never seen one before - what is the intended purpose of the device?

Their purpose is to contain fuel vapours within the tank so that they vent through the proper channels and not out the gas cap.  This was a California clean air requirement.

Chaos @k100-forum wrote:
Flappers originally had nothing to do with sealing or vapors, they were there to prevent you from putting leaded gas into a vehicle that required unleaded.  The unleaded nozzle was thinner and fit into the flapper hole, the leaded nozzle was too thick to fit.  Another benefit on the K bike is it prevents topping the tank, leaving a bit of air space at the top which might allow a full tank to deform in a crash without bursting.  Automobile tanks are also designed with an air space for that reason.

I have a different purpose in mind.  For some strange reason, liquid gasoline finds its way past the sealing rings on the cap and onto the paint around the lid on my tank.  This deteriorates the paint badly.  I repainted my tank this past winter and already the paint has started to peel off around the lid in under one riding season.  I replaced all the rubber parts in the lid at the same time as painting hoping that new seals would stop the problem.  They didn't.  So, I will depend on the flapper to act as a check valve to prevent sloshing gasoline from migrating past the cap.

Thanks for the info on the flap. Hope it works for you in regard to preserving the paintwork.

Cheers

robmack wrote:

Gaz wrote:Rob, I'd seen references to a fuel tank flap over the years but had never seen one before - what is the intended purpose of the device?

  This was a California clean air requirement.
For some strange reason, liquid gasoline finds its way past the sealing rings on the cap and onto the paint around the lid on my tank. . . . I replaced all the rubber parts in the lid at the same time as painting hoping that new seals would stop the problem. . . .

Have you verified that your tank's vent port is clear?

Laitch wrote:Have you verified that your tank's vent port is clear?

Yes Laitch, I have gone through that verification. Blown air through the tubes.

Yes, it's not the vent.  I've had two bricks with repaints go bad around the filler as well.  Both had good gaskets and clear vents.  All I can find is that there is seepage somewhere in the cap when the bike is on the sidestand with a full tank.  It doesn't seem to take much to mess up the paint there.  A  barely visible drop of gas from time to time is enugh.

Factory paint doesn't have the problem because it's probably urethane based whereas most aftermarket paint jobs are cleared with acrylic based paint.  I suppose if you want to enjoy really serious poison you could clear with urethane to prevent the funk.

Flapper appears to also have a vent hole (or is it a drain hole) that may also allow fuel into the cap ??

There's something evil with gasoline these days.  My tank was professionally painted.  I selected the base coat paint myself and it was a solvent based solution.  The primer coat was 2-part epoxy; the clear coat was 2-part acrylic, again professionally applied. The touchup I had done in the winter was performed by one of the most recognised painters in the Toronto area, so I know the workmanship was top notch.

I wish that I had known about this.
The new paint on my tanks is already deteriorated on the left side of the cap. It was good quality paint with epoxy primer and many coats of clear.

The seal on gas tank itself (not the cap) in pic doesn't appear to have a water drain hole (and i guess this also acts as a fuel/water drain hole) could this be retaining fuel/water around the cap  and causing problems ? Isn't the drain hole on the left side of the tank filler?

norton71 wrote:The seal on gas tank itself (not the cap) in pic doesn't appear to have a water drain hole (and i guess this also acts as a fuel/water drain hole) could this be retaining fuel/water around the cap  and causing problems ? Isn't the drain hole on the left side of the tank filler?

Yes the drain hole is on the left of the tank cap, but I think the cap gasket is not doing its job and fumes are coming out. I've seen that on many Ks.

norton71 wrote:The seal on gas tank itself (not the cap) in pic doesn't appear to have a water drain hole . . .

According to the original post, the pic of the tank is a random one chosen from the Web to show the flapper. It isn't a pic of the tank that is on rbm's moto.

A couple of my mates bikes with non OEM paint jobs and known to have run ethanol have paint problems around the filler.
A couple more of his bikes with OEM paint and also known to have run ethanol have no problems, with the paint. However all four have destroyed their pumps and dampers. My bike has never run on ethanol and OEM paint is fine, OEM pump and damper fine, replacement pump and damper fine.
Regards Martin.

Go back to my post #11.  Most aftermarket paint shops use acrylic based paint and clear coat.  The factory probably uses urethane.

Urethane paints are very toxic and require expensive safety stuff.  Acrylic isn't as bad so is cheaper to setup for, and the paint itself is cheaper too.  A factory paint shop uses enough paint to justify the cost of using urethane, not so much a small independent shop.

Urethane is a lot tougher which would explain the fact that the problems don't show with it.

With the problem bound to reoccur with acrylic clear coat, it would probably be better to source a shop that does urethane.
It would be cheaper in the long run.
Regards Martin.

Would it be possible to share a photo of your tank Rob?  I sprayed my bike early in the summer with a post cat single stage poly enamel (catylised epoxy primer to start).  Nothing nasty to it in terms of handling and spraying and my 'booth' is just my shop cleaned out with a large exhaust fan.  The paint I used is a commercial Sikkens product supplied by a friend who is a technical advisor for a large auto body supplier.  I am definitely burning ethanol more often than not and haven't had any paint issues yet.  I'll ask my friend if he knows of any paint issues like this.  Most shops stick to one brand of paint products.  Would you happen to know what brand was used on your tank?

Hi Woodie,

Here is a picture of the damage to the paint on the tank.



That area of the paint was touched up this past winter. The painter cleared away the other damage to the bare metal, applied epoxy primer, flatted and painted the area. He then top coated. It looked flawless in April this year.

The part arrived today. Thank you so kindly for sending it.

Thanks for posting that Rob.  That spot is right beside the drain hole on the left side under the cap.  Of course after you started this thread and after our meet up in Youngstown I noticed a similar brown colour developing in exactly the same spot on my tank.  It isn't that far along and I was hoping it was coincidental but now I'm none too sure of that.  I'll show your picture and my tank to the friend I mentioned up thread.  Not only is he a coatings expert, he is also a rider and had his own side business custom painting bikes.  I'll let you know what he has to say.  Here's to hoping there is an easy solution for this.

norton71 wrote:The seal below the tank filler cap and the tank itself appears to have a large gap between the tank and the filler cap base which with water
/fuel may cause rust and discoloration.......gap doesn't seem to  exist at the far left and the far right of the seal but you can see gaps in between just over where the water/fuel drain hole is ..is the drain hole clear ?....From memory i poked some 0.9 mm gasless mig wire through the drain hole to verify hole was clear, but wonder why there is a gap when either end appears to be sealed ? Almost looks like three tack welds instead of a continous seal/weld  ? cheers

Thanks Norton,

All the seals on the cap and on the base are brand new.  The gap is a result of the angle at which I took the picture.  I can assure you that there is no gap in or around the water drain hole.  I haven't ridden in any rain this season and I have only done only 1,700 km since May.  I'm fairly certain that the water drain is clear and free but I will take a wire as you did to double-check. That welding around the neck has always looked suspicious to me too.  This particular tank has been repainted twice in its life - once by a previous owner and once by me. When I bought the bike, this deterioration around the water drain hole was present.  I still have no clear idea why this deterioration happens.  I'll try to get a couple more pictures up on the thread, taken from different angles.

UPDATE: I'm adding some pictures. First, the tank when I received it after repainting in March 2018.
https://photos.app.goo.gl/GENg897Wnf11J9e88
https://photos.app.goo.gl/rZCR4JYoSAz8RAVR9
https://photos.app.goo.gl/9xtUzFsuiic4mg7W9

Now, some closeups of the deterioration in as little as 5 months.
https://photos.app.goo.gl/NbGMiofbAKj7vM1u6
https://photos.app.goo.gl/pehFR55tS1e7XRJf8
https://photos.app.goo.gl/wKuwJUTDsyYmeZrV9
https://photos.app.goo.gl/QifhfX3j5mmhnkdn8
https://photos.app.goo.gl/toiLF9BJ58awEsdQ9

Hi ..sent a pm to you Rob ..maybe of some use?